Apparatus for measuring compression pressures in internal-combustion engine

Abstract

An apparatus for detecting and indicating the pressure under which the air-fuel mixture is compressed in an internal-combustion engine for automobile vehicles, and more particularly an apparatus of the type which comprises probe means adapted to detect a compression pressure exerted during the compression stroke in the combustion chamber, and a plurality of electric circuits for processing signals from the probe means and indicating on display means the compression pressure as detected.

What is claimed: 
     
       1. An apparatus for measuring a pressure under which the air-fuel mixture is to be compressed during the compression stroke in the combustion chamber of an automobile internal-combustion engine, said apparatus comprising probe means including resistor means for detecting a secondary voltage signal consisting of a capacity discharge voltage signal, an induced discharge voltage signal and a free-oscillating discharge voltage signal from an ignition system, which probe means having one end connected to a secondary terminal of a secondary winding of an ignition coil and the other end connected to a rotor of a distributor which is connected to said secondary terminal of said secondary winding; a plurality of electric circuits connected to said probe means for selecting only said induced discharge voltage signal from said secondary voltage signal detected by said probe means, electrically processing said induced discharge voltage signal and indicating the value of said induced discharge voltage as the compressed pressure in the combustion chamber in a readable form. 
     
     
       2. The apparatus according to claim 1, wherein said plurality of electric circuits include a gating circuit actuated to select said desired signal from said secondary-voltage signal, a peak-hold circuit actuated to hold a voltage level of said desired signal during a given period of time, a display unit operated to indicate an output of said peak-hold circuit, a gate-signal generating circuit actuated in synchronism with each occurrence of said secondary-voltage signal for generating and feeding a gate signal to said gating circuit, and a reset circuit actuated in synchronism with each occurrence of said secondary-voltage signal for resetting said voltage level of said desired signal held in said peak-hold circuit. 
     
     
       3. The apparatus according to the claim 2 wherein said gating circuit includes a differential-type operational amplifier, and FET having a source terminal connected to an output terminal of said differential-type operational amplifier, a drain terminal connected to an input terminal of said peak-hold circuit and a gate terminal connected to an output terminal of said gate-signal generating circuit. 
     
     
       4. The apparatus according to the claim 3 wherein said gating circuit includes at the pre-stage thereof an amplifier of high input impedance and adapted to receive said secondary-voltage signal, and a low-pass filter actuated to remove all noises from said secondary-voltage signal. 
     
     
       5. The apparatus according to the claim 4 wherein said low-pass filter includes a Butterworth filter. 
     
     
       6. The apparatus according to the claim 2 wherein said peak-hold circuit includes a first FET controllable by an output of said gating circuit, and a second FET actuated upon receipt of a reset signal from said reset circuit to reset said voltage level held in said peak-hold circuit. 
     
     
       7. The apparatus according to the claim 6 wherein said peak-hold circuit is connected to an integrating amplifier including an integrating circuit actuated to convert said voltage level held in said peak-hold circuit into a d.c. voltage signal. 
     
     
       8. The apparatus according to the claim 2 wherein said display unit includes an analog meter. 
     
     
       9. The apparatus according to the claim 2 wherein cable means is provided for connecting a primary winding of said ignition coil with said gate-signal generating circuit and said reset circuit for feeding a signal synchronizing with a primary voltage signal from said ignition system to said gate-signal generating circuit and said reset circuit. 
     
     
       10. The apparatus according to the claim 9 wherein there are provided a low-pass filter actuated to remove all noises from said primary-voltage signal, and a waveform shaper circuit actuated to shape an output of said low-pass filter for feeding an output of said waveform shaper circuit to said gate-signal generating circuit and said reset circuit. 
     
     
       11. The apparatus according to the claim 10 wherein said waveform shaper circuit includes a Schmidt circuit. 
     
     
       12. The apparatus according to the claim 2 wherein said gate-signal generating circuit includes a monostable multi-circuit. 
     
     
       13. The apparatus according to the claim 2 wherein said gate-signal generating circuit includes a delay circuit and a monostable multi-circuit. 
     
     
       14. The apparatus according to the claim 1 wherein said probe means includes a body of electrically insulating material and having a holder portion integrally therewith, a conductor member fixedly disposed within said body and having one end thereof detachably connectable with said secondary terminal of said ignition coil and the other end thereof detachably connectable with a wire of an ignition coil, and a potential divider fixedly disposed within said body and including a plurality of resistance elements connected with each other and having one end thereof connected to said conductor member and an output terminal at the other end thereof. 
     
     
       15. The apparatus according to the claim 1 wherein said plurality of electric circuits include a switching circuit actuated to separate a series of outputs from said operational circuit into an individual signal for each cylinder. 
     
     
       16. The apparatus according to the claim 15 wherein said switching circuit includes a plurality of gating circuits of a number corresponding to the number of said cylinders and adapted to receive a series of output signals from said switching circuit, a trigger probe for detecting presence of said secondary voltage when said secondary voltage is applied to any one of said cylinders, a reset circuit actuated to supply a synchronizing signal received from said trigger probe to any one of said gating circuits for said any one of said cylinders, a register circuit resettable by said reset circuit and adapted to receive said primary-voltage signal, and a logic circuit for supplying an output of said register circuit to each of the other gating circuits of said gating circuits. 
     
     
       17. The apparatus according to the claim 16 wherein said trigger probe includes an induction coil. 
     
     
       18. The apparatus according to claim 2, wherein said reset circuit includes a differentiating circuit and a waveform shaper circuit. 
     
     
       19. The apparatus according to claim 2, wherein said reset circuit includes a differentiating circuit, a waveform shaper circuit and a switching circuit. 
     
     
       20. An apparatus for measuring a pressure under which the air-fuel mixture is to be compressed during the compression stroke in the combustion chamber of an automobile internal-combustion engine, said apparatus comprising probe means having one end connected to a secondary terminal of a secondary winding of a secondary coil and the other end connected to a distributor rotor in an ignition system for detecting a secondary-voltage signal from said ignition system, and a plurality of electric circuits for selecting an induced discharge voltage signal from said secondary-voltage signal detected by said probe means, electrically processing said induced signal and indicating said induced signal in readable form, a frequency-to-voltage converter circuit adapted to convert a frequency of a primary-voltage signal from said ignition system into a voltage-level signal for supplying a d.c. voltage signal which is proportional to the number of revolutions of the engine, and an operational circuit actuated to compute an output of said frequency-to-voltage converter circuit and said voltage level of said induced discharge voltage included in said secondary voltage signal for supplying an output to represent a compression pressure exerted and detected at each top dead point of the piston.